Technical Information Threading Recommendation for Threading Infeed Passes TPI 48–32 28–24 20–16 14–12 11.5–9 8–6 5–4 3–2 metric pitch (mm) 0,50–0,75 0,80–1 1,25–1,5 1,75–2 2,5–3 3,5–4 4,5–6 8 Thread Type recommended number of passes Common V-thread forms ISO, UN, UNJ, NPT, Whitworth, BSPT, API Rotary Shoulder 4–5 5–6 6–8 8–10 9–12 12–15 14–16 15–25 Acme, Trapez, Round, API Round — — 5–6 7–8 10–11 12–13 13–15 18–20 Stub Acme, API Buttress — — 5 5–6 7–8 8–10 10–12 14–16 American Buttress — — 7–8 9–10 11–12 13–15 17–19 22–24 Maintain minimum 0,05mm infeed on last passes to avoid work hardening and excessive abrasion of the threading tool. Constant Volume Infeed Values for Threading Operations In most applications, use of CNC canned cycles produces only marginally Formula for constant chip load infeed successful results. For example, an 8-pitch external thread has a depth of 2mm (.0789"). 6ap = radial infeed x = actual pass (from 1 to the nap) nap = number of passes q = 1st pass, 0.3 6apx = ap * q 2nd pass, 13rd pass and up, x-1 nap-1 Using Radial Infeed Using Flank Infeed Bending stress on the cutting edge caused by V-shaped chips Lower bending stress and stabilised cutting edges produce from long-chipping steel workpiece materials. more favourable chip shapes and larger cutting thicknesses. High cutting forces with small cutting thicknesses require sharp Carbides with high hardness, good wear resistance, edges with high strength. and temperature stability are advantageous. Guidelines for Infeeds — How to Determine the Number and the Size of Passes The number of passes “s” per thread is decisive for successful threading If insert breakage occurs, the number of passes must be increased. With and crest turning. The following tables give standard values for the increased wear, we recommend decreasing the number of passes. The chip application condition when machining steel. The proper number thickness should not be less than 0,05mm. The allowance at the diameter of passes must be determined empirically. should not exceed 0,2mm. widia.com F87